250 



ROBERT W. HEGNER. 



The last egg selected from this series was fixed three days after 

 the operation at an age of five days. It indicates that develop- 

 ment of the living part of the embryo proceeds up to the time of 

 hatching. 



7. KILLING PARTS OF AN OLD EMBRYO. 



The eggs used for these experiments were laid at 4 P.M. 

 June 17, and operated upon at 4 P.M. June 20, at the age of 

 three days. Part of them were kept as controls; the rest were 

 divided into two lots and operated upon as indicated in Table VI. 

 The control eggs hatched on June 22. 



TABLE VI. 



EXPERIMENTS IN KILLING PARTS OF OLD EMBRYOS. 

 Lepiinolarsa decemlineata Series L.D. 06. 



Fig. 6 shows a normal embryo fixed at the time of the operation. 

 The eggs under experimentation were fixed at intervals and 

 stained and mounted. In every case the part of the embryo 

 that remained alive continued to develop. This was true for 

 both those with the anterior part and those with the posterior 

 part killed. There were no signs of regeneration even after the 

 normal embryonic period had passed. The killed part of the 

 embryo began to disintegrate immediately after the operation. 



8. SUMMARY. 



i. If the region of a freshly laid egg of Leptinotarsa decem- 

 lineata, which contains the germ cell determinants (Fig. I, gcd), 

 is killed with a hot needle and these granules are thus prevented 

 from taking part in embryonic development, the embryo pro- 

 duced by the rest of the egg lacks the germ cells. This supple- 



